Compact heat-generating devices, such as laser diodes, light-emitting diodes (LEDs), vertical-cavity surface emitting lasers (VCSELs), integrated circuits including microprocessors, microwave chips and the like, generate thermal energy, or heat, when in operation. Regardless of which type of heat-generating device the case may be, heat generated by a compact heat-generating device needs to be removed or dissipated from the compact heat-generating device in order to achieve optimum performance of the compact heat-generating device and keep its temperature within a safe operating range. With the form factor of compact heat-generating devices (e.g., sensors or ASIC drivers in a telecom router, cellular phone tower, data communications server or mainframe computers) and the applications they are implemented in becoming ever smaller (e.g., the processor in a smartphone, a tablet computer or a notebook computer) resulting in high heat density, it is imperative to effectively dissipate the high-density heat generated in an area of small footprint to ensure safe and optimum operation of compact heat-generating devices operating under such conditions.
Many metal-based water-cooled and air-cooled cooling packages have been developed for use in compact packages to dissipate heat generated by the various types of compact heat-generating devices mentioned above. For instance, heat exchangers and heat pipes made of a metallic material with high thermal conductivity, such as copper, silver, aluminum or iron, are commercially available. However, most metal-based heat exchangers and heat pipes experience issues of oxidation, corrosion and/or crystallization after long periods of operation. Such fouling factors significantly reduce the heat transfer efficiency of metal-based heat exchangers and heat pipes. Other problems associated with the use of metal-based cooling packages include, for example, issues with overall compactness of the package, corrosion of the metallic material in water-cooled applications, difficulty in manufacturing, and so on. With increasing demand for high power density in small form factor, there is a need for a compact cooling package for compact heat-generating devices with fewer or none of the aforementioned issues.
One issue with heat dissipation in portable/mobile applications is that, even when heat generated by a heat-generating device (e.g., the processor in a smartphone, a tablet computer or a notebook computer) is removed or otherwise transferred away from the heat-generating device, the heat more or less is transferred to other portions of the portable apparatus in which the heat-generating device resides. This may not be desirable especially in portable/mobile applications. For instance, at least a portion of the heat generated by a microprocessor in a notebook computer is transferred to the casing of the notebook computer (e.g., a portion of the computer's casing closest to the microprocessor) making the casing warm or even hot to touch. As another example, some notebook computers may have a cooling fan installed therein to promote heat transfer by convection to cool off the microprocessor of the notebook computer. Still, warm air can be felt near a vent of the casing where the cooling fan blows hot air out of the casing, and the casing of the notebook computer may still be warm or even hot to touch. Consequently, user experience of such portable/mobile apparatus may be negatively impacted if not rendered dangerous.